Great mechanical power is needed when solid particles are introduced into liquid medium. In addition, after the solid particles are dispersed into the liquid medium, they are attached to each other and can re-congregate due to London force/van der waals force, and hence the stability of the dispersion is destroyed. Therefore, a dispersant is often introduced to improve the efficiency when solid particles enter liquid medium and to enhance the stability of the dispersion.
A dispersant is a surfactant which possesses both hydrophobicity and hydrophilicity in the molecule. A part of its structure has an anchoring group with relatively high polarity that can be easily attached onto the surface of the solid particles, whereas the other part is a long molecular chain with relatively low polarity, which has high affinity to the dispersion medium (solvent or resin). Therefore, the dispersant can evenly disperse the solid particles of inorganic or organic paint which are difficult to be dissolved into liquid. In the meantime, it can also prevent the solid particles from sedimentation and congregation, and promote a relatively stable suspension.
With the wide application of organic paint and carbon black in the field of painting, ink and plastics, high molecular weight dispersants, such as polyacrylic ester or polyurethane, has become an indispensable additive to fundamentally improve the stability of these paints in the liquid. Since polyurethane has a special polymeric isocyanate core and high reactive activity with NCO, it can react with mono alcohols with different polarities and form steric chain segments, and therefore it can easily improve the stability of organic paint. It is no longer problem for a high molecular dispersant with high compatibility to have a stable dispersion of organic paint with high qualities.
U.S. Pat. No. 4,032,698 mentions a kind of polyurethane dispersant which is prepared using isocyanate polymers with 2.5 to 6 functionalities, monohydroxyl compounds of polyacrylic ester and anchoring terminal groups, wherein the anchoring terminal groups are alkalic reactants having —SH, —OH or —NH2 or other reactive groups, such as dicyandiamide, dinitraniline, diaminomaleonitrile, 3-amino-1,2,3 triazole, etc.
EP154678 discloses a polyurethane dispersant, which is prepared using isocyanate polymers, hydroxyl compounds, and a compound containing a zerewitinoff reactive hydrogen and at least an alkalic group with nitrogen. This reactive hydrogen containing compound used as anchoring terminal group is preferably —NH2 containing heterocyclic compounds, such as 1-(2-Aminoethyl)piperazine, 3-amino-1,2,4-triazole, 4-(2-aminoethyl)-pyridine, etc.
WO97/26984 discloses a polyurethane dispersant. Besides isocyanate polymers and hydroxyl compounds, the anchoring terminal group used is a Michael addition product, such as the addition product of a heterocyclic compound that contains reactive hydrogen and hydroxy-propyl (ethyl) acrylate, or the addition product of a heterocyclic product containing reactive hydrogen and glycidyl ether.
The polyurethane dispersant in CN200780044910 also uses a Michael addition anchoring terminal group to react with alkylaminoalkylamine and α,β-unsaturated carbonyl compound containing hydroxyl group.
The polyurethane dispersant in EP2007/05145 uses unsaturated mono hydroxyl compound as anchoring terminal group, such as propargyl alcohol, furfurylalcoho, etc, and the final product does not have amine value.
The polyurethane dispersants above use different kinds of anchoring terminal groups, which can disperse inorganic and part of organic paints well. However, to certain organic paint, such as cyanine. Isoindoline and carbon black, there exist still the drawbacks of low coloring strength and low stability of storage.